TWI873174B - Systems and methods for purifying solvents - Google Patents

Abstract

The present disclosure is directed to methods and systems of purifying solvents. The purified solvents can be used for cleaning a semiconductor substrate in a multistep semiconductor manufacturing process.

Description

System and method for purifying solvents

Cross-references to Related Applications

This application claims priority to U.S. Provisional Patent Application Serial No. 62/895,198 filed on September 3, 2019, the entire text of which is hereby incorporated by reference. Field of Invention

The present invention relates to a system and method for purifying solvents (e.g., organic solvents). In particular, the present invention relates to a system and method that can be used to obtain organic solvents with high purity, low on-wafer particle counts and/or low on-wafer metal counts.

Invention Background

The semiconductor industry has achieved rapid improvements in the integration density of electronic components due to the continued reduction in component size. The result is that more smaller components can be integrated into the area provided. Most of these improvements are due to the development of new precision and high-resolution processing technologies.

During the manufacture of high-resolution integrated circuits (ICs), a variety of processing fluids come into contact with bare or film-coated wafers. For example, the manufacture of fine metal interconnects typically includes a process of coating a base material with a pre-wetting fluid before using a composite fluid to coat the base material to form a resistive film. These processing fluids include proprietary compositions and various additives that are known sources of contamination of IC wafers.

It can be speculated that even if trace amounts of contaminants are mixed into these chemical liquids such as wafer pre-wetting liquid or developer solution, the resulting circuit pattern may have defects. The presence of very low levels of metal impurities, such as as low as 1.0 ppt, is known to interfere with the performance and stability of semiconductor devices. Depending on the type of metal contaminant, oxide properties may be degraded, inaccurate patterns may be formed, and the electrical performance of the semiconductor circuit may be weakened, which ultimately adversely impacts manufacturing yields.

Contaminants such as metallic impurities, fine particles, organic impurities, moisture and the like can be inadvertently introduced into the chemical liquid during various stages of its manufacture. Examples include the following: the impurities are present in the raw materials, or are byproducts or residual unreacted reactants generated when the chemical liquid is manufactured, or are foreign substances hidden or introduced from the surface of the manufacturing equipment or from the container equipment, reaction container or the like used during transportation, storage or reaction. Therefore, reducing or removing insoluble and soluble contaminants from these chemical liquids used to manufacture high-precision and ultra-fine semiconductor electronic circuits is a basic guarantee for the manufacture of defect-free ICs.

In this regard, it is necessary to significantly improve and strictly control the standards and quality of the chemical liquid manufacturing method and system to form a high-purity chemical liquid, which is indispensable in the manufacture of ultra-fine and extremely precise semiconductor electronic circuits.

Summary of the invention

Therefore, in order to form high precision integrated circuits, the need for ultrapure chemical liquids and the quality improvement and control of these liquids has become very critical. Targets for specific key parameters of quality improvement and control include: reduction of metals in the liquid and on the wafer, reduction of particle counts in the liquid and on the wafer, reduction of defects on the wafer, and reduction of organic contaminants. All of these key parameters have been shown to be affected by the necessary preparation of the purification system and the appropriate design of the purification method.

In view of the above, the present invention particularly provides a purification system and method for purifying a solvent (e.g., an organic solvent) for use in preparing a solvent targeted for semiconductor manufacturing, which produces an ultrapure solvent in which the number of particles and the amount of metal impurities in the solvent are controlled within a predetermined range and no unknown and unwanted substances are generated or introduced. Therefore, the occurrence of residues and/or particle defects is suppressed and the yield of semiconductor wafers is improved. Furthermore, the inventors unexpectedly discovered that using a relatively large number of filters having relatively small average pore sizes and arranged in parallel to purify a solvent can produce a process having a relatively high flow rate (e.g., higher than known processes using filters having relatively small average pore sizes that are not parallel but arranged in series), which in turn increases the throughput of the purification system.

In one aspect, the present invention is a method for purifying an organic solvent, which includes passing the organic solvent through a first filter unit and a second filter unit downstream of the first filter unit to obtain a purified organic solvent. The first filter unit includes a first housing and at least one first filter in the first housing, and the first filter includes a filter medium with a first average pore size. The second filter unit includes a second housing and at least two second filters in the second housing, the at least two second filters are arranged in parallel in the second housing, and each second filter independently includes a filter medium with a second average pore size. The number of first filters in the first filter unit is less than the number of second filters in the second filter unit, and the first average pore size is larger than the second average pore size.

In another aspect, the present invention is a system comprising a first filter unit and a second filter unit downstream of the first filter unit and in fluid communication with the first filter unit. The first filter unit comprises a first housing and at least one first filter in the first housing, and the first filter comprises a filter medium having a first average pore size. The second filter unit comprises a second housing and at least two second filters in the second housing, the at least two second filters are arranged in parallel in the second housing, and each second filter independently comprises a filter medium having a second average pore size. The number of first filters in the first filter unit is less than the number of second filters in the second filter unit, and the first average pore size is larger than the second average pore size.

Specific examples may include one or more of the following features.

In some embodiments, the methods described herein may further include passing the organic solvent through a third filter unit disposed between the first and second filter units, wherein the third filter unit includes a third housing and at least one third filter in the third housing, the third filter includes a filter medium having a third average pore size, and the filter medium in the third filter includes an ion exchange membrane.

In some embodiments, the methods described herein may further include passing the organic solvent through and out of the second filter unit to a storage tank. In some embodiments, the methods described herein may further include recirculating the organic solvent by moving the organic solvent from the storage tank to the first filter unit and passing the organic solvent through the first and second filter units. In some specific examples, the method described herein may further include allowing the organic solvent to pass through a fourth filter unit disposed downstream of the second filter unit, wherein the fourth filter unit includes a fourth housing and at least two fourth filters in the fourth housing, the at least two fourth filters are arranged in parallel in the fourth housing, and each of the fourth filters independently includes a filter medium having a fourth average pore size.

In some embodiments, the methods described herein may further include recirculating the organic solvent by moving the organic solvent exiting the fourth filter unit to the storage tank and then passing the organic solvent through the fourth filter unit. In some embodiments, the methods described herein may further include moving the purified solvent to a packaging station disposed downstream of the fourth filter unit.

In some embodiments, the passing an organic solvent is performed at a flow rate of about 25 to about 170 L/min.

In some specific examples, the first filter unit includes one first filter. In some specific examples, the second filter unit includes two or three second filters. In some specific examples, the third filter unit includes one to three third filters. In some specific examples, the fourth filter unit includes 4 to 14 fourth filters.

In some embodiments, the first average pore size is about 50 nm to about 200 nm. In some embodiments, the second average pore size is about 10 nm to about 50 nm. In some embodiments, the fourth average pore size is at most about 10 nm.

In some embodiments, the filter medium in the first, second, third or fourth filter includes polypropylene, high density polyethylene, ultra high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer.

In some embodiments, the number of second filters in the second filter unit is less than the number of fourth filters in the fourth filter unit.

In some embodiments, the fourth average pore size is smaller than the second average pore size.

In certain specific examples, the organic solvent includes cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 4-methyl-2-pentanol or propylene carbonate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As defined herein, unless otherwise stated, all percentages expressed are to be understood as weight percentages relative to the total weight of the composition. Unless otherwise stated, ambient temperature is defined as being between about 16 and about 27° C. Unless otherwise stated, the term “solvent” as used herein refers to a single solvent or a combination of two or more (e.g., three or four) solvents. In the present invention, “ppm” means “parts per million,” “ppb” means “parts per billion,” and “ppt” means “parts per trillion.”

Generally speaking, the present invention features a system and method for purifying a solvent (e.g., an organic solvent). The solvents referred to herein can be used as wafer processing solutions (such as pre-wetting liquids, developer solutions, rinse solutions, cleaning solutions, or stripping solutions), or as solvents for semiconductor materials used in semiconductor manufacturing processes.

Before the purification method of the present invention is performed, the solvent may include unwanted amounts of contaminants and impurities. After the solvent is treated by the purification method of the present invention, substantial amounts of contaminants and impurities may be removed from the solvent. In the present invention, the pre-treated solvent is also referred to herein as "unpurified solvent". The pre-treated solvent may be synthesized in a housing or commercially purchased from a supplier. In the present invention, the treated solvent is also referred to as "purified solvent". "Purified solvent" may include impurities limited to a predetermined range.

Generally speaking, the solvents mentioned herein may include at least one (eg, two, three, or four) organic solvents. Examples of suitable organic solvents include methanol, ethanol, 1-propanol, isopropanol, n-propanol, 2-methyl-1-propanol, n-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-pentanol, 3-pentanol, n-hexanol, cyclohexanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, 2,2-dimethyl-3-pentanol, 2,3-dimethyl-3-pent ... -pentanol, 2,4-dimethyl-3-pentanol, 4,4-dimethyl-2-pentanol, 3-ethyl-3-heptanol, 1-heptanol, 2-heptanol, 3-heptanol, 2-methyl-2-hexanol, 2-methyl-3-hexanol, 5-methyl-1-hexanol, 5-methyl-2-hexanol, 2-ethyl-1-hexanol, methylcyclohexanol, trimethylcyclohexanol, 4-methyl-3-heptanol, 6-methyl-2-heptanol, 1-octanol, 2-octanol, 3-octanol, 2-propyl-1-pentanol, 2,6-dimethyl-4-heptanol, 2-nonanol, 3,7-dimethyl-3-octanol, ethylene glycol, propylene glycol, diethyl ether, dipropyl ether, diisopropyl ether, butyl methyl ether, butyl ethyl ether, butyl propyl ether, dibutyl ether, diisobutyl ether, tertiary butyl methyl ether, tertiary butyl ethyl ether, tertiary butyl propyl ether, ditertiary butyl ether, diamyl ether, diisoamyl ether, cyclopentyl methyl ether, cyclohexyl methyl ether, bromomethyl methyl ether, α,α-dichloromethyl methyl ether, chloromethyl ethyl ether, 2-chloroethyl methyl ether, 2-bromoethyl methyl ether, 2,2-dichloroethyl methyl ether, 2-chloroethyl ethyl ether, 2-bromoethyl ethyl ether, (±)-1,2-dichloroethyl ethyl ether, 2,2,2-trifluoroethyl ether, ethyl vinyl ether, butyl vinyl ether, allyl ethyl ether, allyl propyl ether, allyl butyl ether, dipropylene ether, 2-methoxypropylene, ethyl-1-propylene ether, cis-1-bromo-2-ethoxyethylene, 2-chloroethyl vinyl ether, allyl-1,1,2,2-tetrafluoroethyl ether, octane, isooctane, nonane, decane, methylcyclohexane, decalin, xylene, ethylbenzene, diethylbenzene, anisin, dibutylbenzene, umbelliferone, dipentene, methyl pyruvate, monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether acetate, ethyl lactate, methyl methoxypropionate, cyclopentanone, cyclohexanone, n-butyl acetate, gamma-butyrolactone, diisoamyl ether, isoamyl acetate, chloroform, dichloromethane, 1,4-dioxane, hexyl alcohol, 2-heptanone, isoamyl acetate, propylene carbonate and tetrahydrofuran.

In some embodiments, the solvent is a pre-wetting liquid. Examples of the pre-wetting liquid include at least one of cyclopentanone (CyPe), cyclohexanone (CyH), monomethyl ether, propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether (PGEE), propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monopropyl ether (PGPE) and ethyl lactate (EL). In other embodiments, the solvent may be a developer solution, such as n-butyl acetate; or a rinse liquid, such as 4-methyl-2-pentanol (MIBC).

In certain embodiments, the pre-treated or unpurified organic solvent may have a purity of at least about 95% (e.g., at least about 96%, at least about 97%, at least about 98%, or at least about 99%). In certain embodiments, the treated or purified organic solvent obtained from the methods described herein may have a purity of at least about 99.5% (e.g., at least about 99.9%, at least about 99.95%, at least about 99.99%, at least about 99.995%, or at least about 99.999%). As referred to herein, "purity" refers to the weight percentage of the solvent, based on the total weight of the liquid. The amount of the organic solvent in the liquid can be measured using a gas chromatography mass spectrometer (GCMS) apparatus.

In certain embodiments, from the viewpoint of improving the manufacturing yield of semiconductor chips, the boiling point of the solvents described herein is up to about 200° C. (e.g., up to about 150° C.) or down to about 50° C. (e.g., down to about 100° C.). In the present invention, the boiling point means the boiling point at 1 atm.

Generally speaking, impurities included in the pre-treated organic solvent may include metallic impurities, particles and other such as organic impurities and moisture.

As described herein, the metal impurities may be in solid form (e.g., simplex metals, metal-containing particulate compounds, and the like). Examples of common metal impurities include heavy metals such as iron (Fe), aluminum (Al), chromium (Cr), lead (Pb), and nickel (Ni); and ionic metals such as sodium (Na), potassium (K), and calcium (Ca). Depending on the metal type, the metal impurities may damage oxide integrity, degrade MOS gate stacks, and reduce device life. In the organic solvent purified by the method described herein, the total trace metal content is preferably within a predetermined range of 0 to 300 ppt (e.g., 0 to 150 ppt) by mass.

In the present invention, a substance having a size of 0.03 microns or larger is referred to as a "particle" or "microparticle". Examples of the particle include dust, dirt, organic solid matter, and inorganic solid matter. The particle may also include colloidal metal atom impurities. The type of easily colloidal metal atoms is not particularly limited, and may include at least one metal atom selected from the group consisting of: Na, K, Ca, Fe, Cu, Mg, Mn, Li, Al, Cr, Ni, Zn, and Pb. In the organic solvent purified by the method described herein, the total number of particles having a size of 0.03 microns or larger is preferably within a predetermined range of at most 100 (e.g., at most 80, at most 60, at most 50, at most 40, or at most 20) per 1 ml of solvent. The number of "particles" in a liquid medium can be counted by a light scattering type liquid particle counter and is referred to as LPC (Liquid Particle Count).

As described herein, the organic impurities are different from organic solvents and are referred to as organic substances, the content of which is 5000 mass ppm or less relative to the total mass of the liquid including the organic solvent and the organic impurities. The organic impurities can be volatile organic compounds present in the ambient air or even in the clean room. Some of the organic impurities originate from the shipping and storage equipment, while some are present in the starting raw materials. Other embodiments of the organic impurities include byproducts and/or unreacted reactants produced when the organic solvent is synthesized.

The total content of organic impurities in the purified organic solvent is not particularly limited. From the viewpoint of improving the manufacturing yield of semiconductor devices, the total content of the organic impurities in the purified organic solvent may be 0.1 to 5000 mass ppm (e.g., 1 to 2000 mass ppm, 1 to 1000 mass ppm, 1 to 500 mass ppm, or 1 to 100 mass ppm). The content of organic impurities in the solvent described herein can be measured using a gas chromatography mass spectrometer (GC-MS) device.

Fig. 1 is a schematic diagram showing the configuration of a purification system according to some specific examples of the present invention. As shown in Fig. 1, the purification system 10 includes a supply unit 20, a first filtration system 110, a storage tank 130, a second filtration system 120 and a packaging station 140, which are all in fluid communication with each other (e.g., through one or more conduits).

Generally speaking, the supply unit 20 (e.g., a tank) is configured to contain or transport a starting material (e.g., a pre-treated or unpurified organic solvent). The starting material can be processed by the purification system 10 to produce or manufacture a purified organic solvent in which the amount of unwanted contaminants (e.g., particulates, organic impurities, metallic impurities) is limited within a predetermined range. The type of the supply unit 20 is not particularly limited as long as it continuously or intermittently supplies the starting material to other components of the purification system 10. In some specific examples, the supply unit 20 may include a material receiving tank, a sensor such as a level gauge (not shown), a pump (not shown) and/or a valve (not shown) for controlling the flow of the starting material. In FIG1 , the purification system 10 includes one supply unit 20. However, in some embodiments, a plurality of supply units 20 may be provided (eg, in parallel or in series) for each type of starting material to be processed by the purification system 10.

The purification system 10 may include at least one first filtration system 110 and at least one second filtration system 120. Generally speaking, the first filtration system 110 performs initial filtration of a starting material (e.g., an unpurified organic solvent) to remove most impurities and/or particles, and the second filtration system 120 performs subsequent filtration to remove residual impurities and fine particles to obtain an ultra-high purity organic solvent.

In some embodiments, the purification system 10 may optionally include a temperature control unit 100 for setting or maintaining the temperature of the organic solvent within a certain temperature range so that the organic solvent maintains a substantially uniform temperature during the purification process. As described herein, the temperature control unit may include but is not limited to a commercial recirculation heating/cooling unit, a condenser, or a heat exchanger, which may be disposed, for example, on a conduit in the purification system 10. The temperature control unit 100 may be assembled, for example, between the supply unit 20 and the first filtration system 110. In some embodiments, the temperature control unit 100 can set the temperature of the organic solvent to up to about 80°F (e.g., up to about 75°F, up to about 70°F, up to about 65°F, or up to about 60°F) or and/or at least about 30°F (e.g., at least about 40°F, at least about 50°F, or at least about 60°F). In some embodiments, because the pumps used in the purification system 10 can generate heat and increase the temperature of the solvent, the purification system 10 can include additional temperature control units (e.g., units 170 and 180 described below) where appropriate to maintain the temperature of the solvent at a predetermined value.

1 , the first filtration system 110 may include a selective temperature control unit 100, a supply port 110a, one or more (e.g., two, three, four, five, or ten) filter units (e.g., units 112, 114, and 116), an outflow port 110b, a selective recirculation conduit 160h, and one or more selective temperature control units 170, all of which are fluidly connected to one another (e.g., through one or more conduits).

In certain specific embodiments, each filter unit in the first filter system 110 may include a filter housing and one or more (e.g., 2, 3, 4, 5, or 6) filters in the filter housing. Each filter may include a filter medium having an average pore size. The filters may be arranged in parallel or in series in the filter housing. During use, when two filters are arranged in parallel, the solvent to be purified passes through the two filters in parallel (i.e., substantially simultaneously). On the other hand, when two filters are arranged in series, the solvent to be purified passes through the two filters sequentially during use. In some embodiments, some filter units may include a plurality of filters arranged in parallel in the filter housing to increase flow rate and improve productivity.

For example, the first filter system 110 shown in FIG1 includes three filter units (i.e., units 112, 114, and 116), each of which includes a filter housing and one or more filters (e.g., filters 112a, 114a, and 116a) in the filter housing. In other specific examples, in addition to the three filter units shown in FIG1, the first filter system 110 may also include other purification modules (not shown).

1 , the filter unit 112 may include one or more filters 112a in the housing, the filter unit 114 may include one or more filters 114a in the housing, and the filter 116 may include one or more filters 116a in the housing, wherein the filters 112a, 114a, and 116a may be different in functionality or nature and provide different purification processes. In some specific examples, certain filters (e.g., 112a, 114a, and 116a) are respectively installed in the corresponding filter units (e.g., 112, 114, and 116), which may have the same or similar purification functions, physical and chemical properties, pore sizes, and/or structural materials. In some embodiments, each filter in the filter unit can be independently selected from the group consisting of a particle removal filter, an ion exchange filter, and an ion adsorption filter.

In some specific examples, the filter unit 112 (also referred to as the first filter unit herein) may include a filter housing (also referred to as the first housing herein) and at least one (e.g., two or three) filters 112a (also referred to as the first filter herein) in the filter housing. In some specific examples, when the filter unit 112 includes two or more filters 112a, the filters 112a may be arranged in parallel.

In some embodiments, the filter 112a can be a particle removal filter to remove relatively large particles from the organic solvent. In some embodiments, the filter 112a can include a filter medium having an average pore size (also referred to herein as a first average pore size) of at least about 200 nanometers (e.g., at least about 180 nanometers, at least about 160 nanometers, at least about 150 nanometers, at least about 140 nanometers, at least about 120, or at least about 100 nanometers) and/or at least about 50 nanometers (e.g., at least about 60 nanometers, at least about 70 nanometers, at least about 80 nanometers, at least about 90 nanometers, or at least about 100 nanometers). Within the above range, it is possible to reliably remove foreign substances such as impurities or agglomerates included in the organic solvent while suppressing clogging of the filter 112a.

Examples of suitable filter materials for the filter 112a include fluoropolymers (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymers (PFA), or modified polytetrafluoroethylene (MPTFE)), polyamide resins such as nylon (e.g., nylon 6 or nylon 66), polyolefin resins (including high-density and ultra-high molecular weight resins) such as polyethylene (PE) and polypropylene (PP). For example, the filter medium in the particle removal filter can be made of at least one polymer selected from the group consisting of polypropylene (e.g., high-density polypropylene), polyethylene (e.g., high-density polyethylene (HDPE) or ultra-high molecular weight polyethylene (UPE)), nylon, polytetrafluoroethylene, or perfluoroalkoxyalkane polymers. The filter made of the above materials can effectively remove foreign substances (e.g., those with high polarity) that may cause residue defects and/or particle defects, and efficiently reduce the content of metal components in the chemical liquid. In some specific examples, the filter unit 112 may include a filter 112a having an average pore size of about 200 nanometers and made from polypropylene.

In some specific examples, the filter unit 116 (also referred to herein as the second filter unit) may include a filter housing (also referred to herein as the second housing) and at least two (e.g., three or four) filters 116a (also referred to herein as the second filter) in the housing. The filter 116a may be a particle removal filter to remove relatively small particles from the organic solvent. In some embodiments, the filter 116a may include a filter medium having an average pore size (also referred to herein as a second average pore size) of at most about 50 nanometers (e.g., at most about 45 nanometers, at most about 40 nanometers, at most about 35 nanometers, at most about 30 nanometers, at most about 25, or at most about 20 nanometers) and/or at least about 10 nanometers (e.g., at least about 15 nanometers, at least about 20 nanometers, at least about 25 nanometers, or at least about 30 nanometers). In some embodiments, the average pore size of the filter medium in the filter 116a may be smaller than the average pore size of the filter medium in the filter 112a. In this embodiment, the filter 116a may be used to remove particles smaller than those removed by the filter 112a.

In some specific examples, the filter 116a in the filter unit 116 may include an ion adsorption film to remove relatively small particles and/or metal ions from the organic solvent. The ion adsorption film may have a porous film material and may have an ion exchange function. Examples of suitable materials that can be used to make ion adsorption films include, but are not limited to, cellulose, diatomaceous earth, membrane materials for microfiltration membranes such as polyamide resins such as nylon (e.g., nylon 6 or nylon 66), polyethylene (e.g., high-density polyethylene or ultra-high molecular weight polyethylene), polypropylene, polystyrene, resins having imide groups, resins having amide groups and imide groups, fluororesins (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymers (PFA) or modified polytetrafluoroethylene (MPTFE)), membrane materials into which functional groups having ion exchange capability are introduced, or the like. For example, the filter 116a may include at least one polymer selected from the group consisting of polypropylene (eg, high density polypropylene), polyethylene (eg, high density polyethylene or ultra high molecular weight polyethylene), nylon, polytetrafluoroethylene, or perfluoroalkoxy alkane polymer.

In some embodiments, at least some (e.g., all) of the filters 116a may be arranged in parallel in the filter unit 116, and the remaining filters 116a (if any) in the filter unit 116 may be arranged in series. When two filters are arranged in parallel, the organic solvent to be purified may pass through the two filters in parallel (e.g., simultaneously). In some embodiments, the number of filters 116a (e.g., those arranged in parallel) in the filter unit 116 may be greater than the number of filters 112a in the filter unit 112. For example, when the filter unit 112 includes one filter 112a, the filter unit 116 may have two or three filters 116a arranged in parallel. Without intending to be bound by theory, it is believed that the advantage of the system 10 having a greater number of filters arranged in parallel in the filter unit 116 than in the filter unit 112 is that it can accommodate increased flow rates and have improved productivity, or maintain the flow rate of the system 10 without increasing the back pressure of the system. Without intending to be bound by theory, it is believed that when the average pore size of the filter medium in the filter 116a is smaller than the average pore size of the filter medium in the filter 112a, the flow rate of the organic solvent through the filter 116a can be reduced compared to the flow rate of the organic solvent through the filter 112a. Therefore, it is believed that having a larger number of filters 116a arranged in parallel can increase the flow rate and productivity of the system 10.

In some embodiments, the filter unit 116 may include three filters 116a arranged in parallel, having an average pore size of about 50 nanometers and made of ultra-high molecular weight polyethylene.

In some embodiments, the purification system 10 may include an optional filter unit 114 (also referred to herein as a third filter unit). In some embodiments, the filter unit 114 may include a filter housing (also referred to herein as a third housing) and at least one (e.g., two or three) filters 114a (also referred to herein as a third filter) in the filter housing. In some embodiments, at least some (e.g., all) of the filters 114a may be arranged in parallel in the filter unit 114 and the remaining filters 114a (if any) may be arranged in series. In some embodiments, the number of filters 114a (e.g., those arranged in parallel) in the filter unit 114 may be greater than the number of filters 112a in the filter unit 112. For example, when the filter unit 112 includes one filter 112a, the filter unit 114 may have two or three filters 114a (e.g., arranged in parallel). Without intending to be bound by theory, it is believed that the system 10 having a greater number of filters arranged in parallel in the filter unit 114 than in the filter unit 112 has the advantage of being able to accommodate increased flow rates and having improved productivity, or maintaining the flow rate of the system 10 without increasing the back pressure of the system.

In some specific examples, the filter 114a in the filter unit 114 may be an ion exchange filter. For example, the filter 114a may include one or more ion exchange resin films to remove charged particles and/or metal ions from the organic solvent. The ion exchange resin film used in the present invention is not particularly limited, and a filter including an ion exchange resin having a suitable ion exchange group fixed to the resin film may be used. An embodiment of this ion exchange resin film includes a strongly acidic cation exchange resin having a chemically modified cation exchange group (e.g., a sulfonic acid group) on the resin film. Examples of suitable resin films include the following, including: cellulose, diatomaceous earth, nylon (resin with amide groups), polyethylene (e.g., high-density polyethylene or ultra-high molecular weight polyethylene), polypropylene, polystyrene, resin with imide groups, resin with amide groups and imide groups, fluororesin (e.g., polytetrafluoroethylene or perfluoroalkoxy alkane polymer) or high-density polyethylene film. In some specific examples, the ion exchange resin film may be a film having an integrated structure of a particle removal film and an ion exchange resin film. Polyalkylene (e.g., PE or PP) films having chemically modified ion exchange groups thereon are preferred. Cationic ion exchange groups are preferred as the ion exchange groups. The filter with ion exchange resin membrane used in the present invention can be a commercially available filter with metal ion removal functionality. These filters can be selected based on ion exchange efficiency and have an estimated pore size in the range of about 100 nm to about 500 nm.

Examples of the shape of the film material include a pleated type, a flat film type, a hollow fiber type, a porous body as described in JP-A Case No. 2003-112060, and the like. Because the ion exchange group is introduced into the film material, it is preferred to use a combination of at least two of a cation exchange group, a chelate exchange group, and an anion exchange group to optimize the impact and selectivity of the component to be removed. Because the ion adsorption film has porosity, it can also remove a portion of fine particles.

In some embodiments, the filter unit 114 may include three filters 114a arranged in parallel and being ion exchange filters made of polytetrafluoroethylene.

In some embodiments, the first filtration system 110 may optionally include a recirculation conduit 160h to form a recirculation loop to recirculate a partially purified organic solvent back to the first filtration system 110 and be processed again by the filter in the first filtration system 110. In some embodiments, the partially purified organic solvent is recirculated at least twice (e.g., at least three times, at least four times, or at least five times) before being transferred to the storage tank 130.

Generally speaking, the storage tank 130 can be any container suitable for storing chemical liquids. In some specific examples, the storage tank 130 can have a suitable volume. For example, the storage tank 130 can have a volume of at least about 1000 liters (e.g., at least about 2000 liters, at least about 3000 liters, or at least about 5000 liters) and/or at most about 30,000 liters (e.g., at most about 25,000 liters, at most about 20,000 liters, at most about 15,000 liters, or at most about 10,000 liters). In some specific examples, the storage tank 130 does not include any agitator or baffle.

In some embodiments, an optional temperature control unit 170 (e.g., a heat exchanger) may be installed along the recirculation conduit 160h. In this embodiment, the temperature control unit 170 may be installed at a temperature of up to about 80°F (e.g., up to about 75°F, up to about 70°F, or up to about 65°F) and/or at least about 30°F (e.g., at least about 40°F, at least about 50°F, or at least about 60°F) so that the partially purified organic solvent is maintained at a temperature of about 80°F or lower when it is recycled back to the first filtration system 110. In the embodiment shown in FIG. 1 , the recirculation conduit 160h is installed on the upstream side of the outflow port 110b of the first filtration system 110. In some specific examples, the recirculation conduit 160h can be assembled on the downstream side of the outflow port 110b. It is understood that pumps and valves can be installed at the plurality of conduits, outflow ports and supply ports of the first filtration system 110, the supply unit 20 and the temperature control unit 100, if necessary.

As in the embodiment illustrated in FIG. 1 , the purification system 110 may optionally include a temperature control unit 170 (e.g., a heat exchanger) assembled between the filter unit 112 and the filter unit 114 to control the temperature of the organic solvent to a maximum of about 80°F (e.g., a maximum of about 75°F, a maximum of about 70°F, or a maximum of about 65°F) and/or at least about 30°F (e.g., at least about 40°F, at least about 50°F, or at least about 60°F) before the organic solvent is charged into the filter unit 114 and processed.

It should also be noted that the location of the temperature control unit 170 is not limited to the embodiment shown above. In some specific examples, the temperature control unit 170 may be assembled upstream of the filter unit 112, between the filter units 114 and 116, or downstream of the filter unit 116. In these specific examples, another temperature control unit may or may not be installed downstream of the filter unit 112 and before the inlet of the subsequent filter unit (e.g., filter unit 114 and/or filter unit 116). The assembly of another temperature control unit downstream of the filter unit 112 is optional, with the proviso that no other means or equipment (e.g., a pump) is introduced or arranged between the filter unit 112 and the subsequent filter (e.g., filter 114 or 116) that can reintroduce heat energy into the organic solvent.

In some embodiments, the filter units 112, 114, and 116 in the first filter system 110 may not include a filter housing, and the filters 112a, 114a, and 116a may be assembled indiscriminately in the first filter system 110. For example, the first filter system 110 may be a multi-stage system including replaceable filters (e.g., 112a, 114a, and 116a) that are linked together in the first filter system 110, and the organic solvent may pass through these filters in series. In these specific examples, the temperature control unit 170 may be assembled at any position upstream of the first ion exchange filter or ion adsorption filter through which the organic solvent will pass or through which it is connected in series. For example, if the first filtration system 110 is enclosed with a particle removal filter A, a particle removal filter B, an ion exchange membrane A, an ion exchange membrane B, and an ion adsorption membrane A in sequence and downstream of its supply port 110a, the temperature control unit 170 may be assembled between the particle removal filter B and the ion exchange membrane A so that the temperature of the organic solvent is adjusted and controlled to about 80° F. or lower before the organic solvent passes through and is processed by the ion exchange membrane A, and by the subsequent ion exchange membrane B and ion adsorption membrane A. It should be noted that the above-mentioned embodiments are for illustrative purposes and are not intended to be limiting.

As shown in FIG1 , the purification system 10 also includes a second filtration system 120 that is between and in fluid communication with the storage tank 130 and the packaging station 140. The second filtration system 120 may include a supply port 120a, one or more (e.g., two, three, four, five, or ten) filter units 122, an outflow port 120b, an optional recirculation conduit 160f, and one or more optional temperature control units 180, all of which are in fluid communication with each other (e.g., via one or more conduits). It is to be understood that pumps and valves may be installed at the multiple conduits, outflow ports and supply ports, and temperature control units in the second filtration system 120, if desired.

In some specific examples, the filter unit 122 (also referred to herein as the fourth filter unit) may include a filter housing (also referred to herein as the fourth housing) and at least two filters 122a (also referred to herein as the fourth filter) in the filter housing. For example, the filter unit 122 may include 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 filters 122a in the filter housing. The second filter system 120 shown in FIG. 1 includes one filter unit 122. In some specific examples, the second filter system 120 may include two or more (for example, three or four) filter units 122. In this embodiment, the filter unit 122 may not have a separate housing, and the filter 122a may be assembled indiscriminately in the second filter system 120. In other embodiments, in addition to the filter unit 122, the second filter system 120 may also include other purification modules (not shown).

In some embodiments, the filters 122a may be different in function or nature and provide different purification processes. In some embodiments, the filters 122a installed in the filter unit 122 may have the same or similar purification function, physicochemical properties, pore size and/or structural material. In some embodiments, each filter 122a may be independently selected from the group consisting of: particle removal filter, ion exchange filter and ion adsorption filter.

In some embodiments, the filter 122a may include an ion adsorption film (such as those described above with respect to the filter 116a) to remove fine charged particles and/or metal ions in the organic solvent to be purified. In some embodiments, the filter 122a may include a filter medium having an average pore size (also referred to herein as a fourth average pore size) of at most about 10 nanometers (e.g., at most about 7 nanometers, at most about 5 nanometers, at most about 3 nanometers, or at most about 1 nanometer) and/or at least about 1 nanometer (e.g., at least about 3 nanometers or at least about 5 nanometers). In some embodiments, the filter 122a can perform both a screening function (e.g., removing fine particles) and an ion exchange function (e.g., removing charged particles and/or metal ions). In some embodiments, the average pore size of the filter medium in the filter 122a can be smaller than the average pore size of the filter medium in the filter 116a. In this embodiment, the filter 122a can be used to remove particles smaller than those removed by the filter 116a.

Examples of suitable materials that can be used in the filter 122a include polypropylene (e.g., high-density polypropylene), polyethylene (e.g., high-density polyethylene or ultra-high molecular weight polyethylene), nylon (e.g., nylon 6 or nylon 66), polytetrafluoroethylene, or perfluoroalkoxyalkane polymers. In some specific examples, the filter 122a and filters 112a, 114a, and 116a described above can be made from non-fluorinated polymers.

In some embodiments, the filters 122a (e.g., ion adsorption filters) may have the same characteristics (e.g., the same pore size) except that they are made from different materials. For example, in some embodiments, when one filter 122a is made from ultra-high molecular weight polyethylene, the other filter 122a may be made from a fluoropolymer (e.g., PTFE). Without intending to be bound by theory, it is believed that using a combination of filters 122a whose filter media are made from different materials can maximize the reduction of impurities, particles, and metal ions to obtain ultra-high purity organic solvents.

In some embodiments, at least some (e.g., all) of the filters 122a may be arranged in parallel in the filter unit 122 and the remaining filters 122a (if any) in the filter unit 122 may be arranged in series. In some embodiments, the number of filters 122a (e.g., those arranged in parallel) in the filter unit 122 may be greater than the number of filters 116a in the filter unit 116. For example, when the filter unit 116 includes three filters 116a, the filter unit 122 may have four or more (e.g., six) filters 122a arranged in parallel. Without intending to be bound by theory, it is believed that the advantage of the system 10 having a greater number of filters arranged in parallel in the filter unit 122 than in the filter unit 116 can accommodate increased flow rates and have improved productivity. Without intending to be bound by theory, it is believed that when the average pore size of the filter medium in the filter 122a is smaller than the average pore size of the filter medium in the filter 116a, the flow rate of the organic solvent through the filter 122a can be reduced compared to the flow rate of the organic solvent through the filter 116a. Therefore, it is believed that having a greater number of filters 122a arranged in parallel can increase the flow rate and productivity of the system 10.

In some embodiments, the filter unit 122 may include six filters 122a arranged in parallel, having an average pore size of about 3 nm and made of ultra-high molecular weight polyethylene.

1 , the second filtration system 120 includes an optional recirculation conduit 160f to form a recirculation loop for recirculating the partially purified organic solvent back to the storage tank 130 and again processed by the filter unit 122 in the second filtration system 120. In certain embodiments, the partially purified organic solvent is recirculated at least twice (e.g., at least three times, at least four times, or at least five times) before completing the purification process and transferring the organic solvent to the packaging station 140. In certain embodiments, without intending to be bound by theory, it is believed that recirculating the partially purified solvent through the second filtration system 120 more than twice may not achieve further improvements in impurity removal. 1, the recirculation conduit 160f is assembled on the downstream side of the outflow port 120b of the second filtering system 120. In other embodiments, the recirculation conduit 160f may be assembled on the upstream side of the outflow port 120b.

In some embodiments, the second filter system 120 may include one or more optional temperature control units 180 (e.g., heat exchangers) at any suitable location. For example, the temperature control unit 180 may be assembled along the recirculation conduit 160f. In some embodiments, the temperature control unit 180 may be assembled between the supply port 120a and the filter unit 122 and between the filter unit 122 and the outflow port 120b. In certain specific examples, the temperature control unit 180 can be configured to maintain the temperature of the organic solvent in the second filtration system 120 at a temperature of up to about 80°F (e.g., up to about 75°F, up to about 70°F, or up to about 65°F) and/or at least about 30°F (e.g., at least about 40°F, at least about 50°F, or at least about 60°F) at about 80°F or lower.

In some embodiments, the packaging station 140 can be a mobile storage tank (e.g., a tank in a tanker) or a fixed storage tank. In some embodiments, the packaging station 140 can be a fluoropolymer-lined device (e.g., an interior surface thereof can include a fluoropolymer, such as PTFE).

The invention also features a method of purifying a solvent (e.g., an organic solvent). Generally speaking, the purification method can include passing the solvent through two or more (e.g., three or four) filter units in the first and second filter systems 110 and 120. For example, referring to FIG. 1 , an unpurified or pre-treated solvent (i.e., a starting material) can be purified by the purification system 10 by allowing the solvent from the supply unit 20 to pass through the filter unit 112, the selective filter unit 114, and the filter unit 116 in the first filter system 110 and be collected in the storage tank 130, and allowing the solvent from the storage tank 130 to pass through the filter unit 122 in the second filter system 120 to the packaging station 140 (e.g., having a volume of about 100 to 1000 liters). In certain embodiments, the purification methods described herein may include recirculating the solvent at least once (e.g., two or three times) through a recirculation loop (e.g., through the storage tank 130, the filter unit 122, and the recirculation conduit 160f) in the second filtration system 120 before transferring the purified solvent to the packaging station 140. In certain embodiments, the purification methods described herein may include recirculating the partially purified solvent at least once (e.g., two or three times) through a recirculation loop (e.g., through filter units 112, 114, and 116 and recirculation conduit 160h) in the first filtration system 110 before transferring the partially purified solvent to the storage tank 130.

In some embodiments, the unpurified or pre-treated solvent may include an organic solvent containing a metal element selected from the group consisting of sodium (Na), potassium (K), aluminum (Al), calcium (Ca), copper (Cu), iron (Fe), chromium (Cr), nickel (Ni) and lead (Pb). In some embodiments, the content of each metal component in the pre-treated solvent ranges from about 0.1 to 1000 mass ppt (e.g., 200 to 1000 mass ppt or 500 to 1000 mass ppt).

1, when the pre-treated solvent reaches the temperature control unit (e.g., unit 100 or any subsequent temperature control unit, such as units 170 and 180), the temperature of the solvent can be adjusted to a predetermined optimal temperature range (e.g., 30°F to 80°F, 30°F to 70°F, 41°F to 67°F, or 50°F to 65°F). For example, the temperature of the solvent can be adjusted to 70°F, 68.5°F, or 67.5°F. In general, the temperature control unit can maintain or adjust the temperature of the solvent at a particular location in the purification system 10 (e.g., before the inlet of the filter) or throughout the entire purification system 10.

When the number of particles and the amount of impurities detected from the purified solvent are controlled within a predetermined range at the end of the treatment by the first and second filtering systems 110 and 120, an ultra-high purity solvent (e.g., including 0.1 to 100 mass ppt of metal components, such as those metal elements selected from the group consisting of iron (Fe), chromium (Cr), nickel (Ni), and lead (Pb)) is produced. Subsequently, the ultra-high purity solvent can be transferred to a packaging station 140 or used in a manufacturing process for manufacturing semiconductor objects.

In some embodiments, the solvents purified by the methods and systems described herein can have a purity of at least about 99.5% (e.g., at least about 99.9%, at least about 99.95%, at least about 99.99%, at least about 99.995%, or at least about 99.999%). In some embodiments, the solvents purified by the methods and systems described herein can form a film or coating having an on-wafer particle count of at most about 500 (e.g., at most about 450, at most about 400, at most about 350, at most about 300, at most about 250, at most about 200, at most about 150, at most about 100, at most about 50, or at most about 25) or 0 on a whole wafer (e.g., a 12-inch wafer). In certain embodiments, the solvent purified by the methods and systems described herein can form a film or coating having a metal count on wafer (e.g., total metal count on wafer or metal count on wafer for a specific metal such as Fe or Ni) of at most about 100 (e.g., at most about 90, at most about 80, at most about 70, at most about 60, at most about 50, at most about 40, at most about 30, at most about 20, or at most about 10) or 0 on a whole wafer (e.g., a 12 inch wafer). In certain embodiments, the solvent purified by the methods and systems described herein can form a film or coating having a defect density (i.e., based on the total number of metals and particles on the wafer) of at most about 1.5 (e.g., at most about 1.4, at most about 1.2, at most about 1, at most about 0.8, at most about 0.6, at most about 0.5, at most about 0.4, at most about 0.2, at most about 0.1, at most about 0.07, at most about 0.05, at most about 0.03, at most about 0.02, at most about 0.01, at most about 0.007, at most about 0.005, at most about 0.004, at most about 0.003) or 0 per square centimeter on the entire wafer (e.g., a 12-inch wafer).

In certain embodiments, the solvent can be purified by the methods and systems described herein at relatively high flow rates. For example, the solvent can be purified at a flow rate (e.g., a flow rate through the first filtration system 110 or a flow rate through the second filtration system 120) of at least about 25 L/min (e.g., at least about 30 L/min, at least about 40 L/min, at least about 50 L/min, at least about 60 L/min, at least about 80 L/min, at least about 100 L/min, or at least about 120 L/min) and/or at most about 170 L/min (e.g., at most about 160 L/min, at most about 150 L/min, at most about 140 L/min, at most about 130 L/min, at most about 120 L/min, at most about 110 L/min, or at most about 100 L/min). In general, the flow rate used to purify the solvent may vary depending on a number of factors, including the nature and viscosity of the solvent to be purified, temperature, the number of filters (e.g., those arranged in parallel), and the type and number of other equipment used in the purification process. Without intending to be bound by theory, it is believed that the flow rate of the solvent to be purified cannot be too high in order to minimize defects on the wafer and minimize electrostatic charge that accumulates on the interior surface of a conduit or container that can corrode the conduit or container.

The present invention will be explained in more detail with reference to the following embodiments, which are used for illustrative purposes and should not be interpreted as limiting the scope of the present invention.

A solvent sample is collected and then loaded into a wafer coating tool. After coating a bare wafer with the sample, the wafer is transferred to a laser-based inspection system and inspected. The laser-based inspection system uses laser light with a detection limit of 19 nanometers to detect, count, and record the location and size of each particle on the wafer. More specifically, the count targets include particles having a size of 19 nanometers or larger. The data is used to generate a wafer map and provide a total on-wafer particle count (OWPC).

The wafer is then transferred to inspection by EDX (Energy Dispersive X-ray). Each particle reported by the laser-based inspection system is inspected by EDX (Energy Dispersive X-ray) to provide the elemental information. Any particle detected that produces a metal signal is counted as a metal particle. The total number of particles with a metal identification signature is totaled and reported as OWMP (On Wafer Metal Particles). General Description of Total Trace Metal Measurements

ICP-MS (Inductively Coupled Plasma Mass Spectrometry (ICP-MS)) was used to test the total trace metal concentration in each solvent sample. Each sample was tested for the presence of 26 metal species using a method developed by Fujifilm, the detection limit is metal specific, but the typical detection limit range is 0.00010-0.030 ppb. The concentration of each metal species was then summed up to produce a value, which is displayed as total trace metals (ppb). Example 1

The solvent purified in this embodiment is n-butyl acetate. Referring to FIG1 , n-butyl acetate is purified using a purification system including a supply unit 20, a first filter system 110, a storage tank 130, and a second filter system 120. The first filter system 110 includes a filter unit 112, a filter unit 114, and a filter unit 116. The filter unit 112 includes a filter 112a, which is a 200 nanometer polypropylene filter. The filter unit 114 includes three ion exchange filters 114a arranged in parallel and made of ultra-high molecular weight polyethylene (UPE). The filter unit 116 includes three filters 116a arranged in parallel and made from 50 nanometer PTFE filters. The second filter system 120 includes a filter unit 122, which includes six filters 122a arranged in parallel and made from UPE. No temperature control unit is used. A recirculation conduit 160f is used, but a recirculation conduit 160h is not used.

The test results are summarized in Table 1 below. Table 1 Pollutants Unit Amount in raw materials Amount in finished product Aluminum PPB 0.051 0.028 Calcium PPB 0.081 0.013 Chromium PPB 0.031 0.009 Copper PPB 0.035 0.005 Iron PPB 0.417 0.008 Lead PPB 0.026 0.004 Nickel PPB 0.073 0.002 Potassium PPB 0.043 0.009 Sodium PPB 0.420 0.025 Particles (＞0.05 microns) Particles/mL ＞10,000 151 Particles (＞0.1 micron) Particles/mL ＞10,000 49 Particles (＞0.15 microns) Particles/mL ＞10,000 25 Particles (＞0.2 microns) Particles/mL ＞10,000 17 Non-volatile organic residues PPM 0.018 0

As shown in Table 1, the total amount of trace metals, particles and non-volatile organic residues in the raw material (pre-purification) has been significantly reduced using the above purification system.

Although the invention has been described in detail with reference to certain specific examples thereof, it will be understood that the invention encompasses modifications and variations within the spirit and scope of what has been described and claimed.

10: Purification system 20: Supply unit 100,170,180: Temperature control unit 110: First filter system 112,114,116,122: Filter unit 112a,114a,116a,122a: Filter 110a,120a: Supply port 110b,120b: Outflow port 120: Second filter system 130: Storage tank 140: Packaging station 160f,160h: Recirculation duct

FIG. 1 is a schematic diagram showing an embodiment of a purification system used in a method for purifying an organic solvent in some embodiments according to the present invention.

10: Purification system

20: Supply unit

100,170,180: Temperature control unit

110: First filter system

112,114,116,122:Filter unit

112a,114a,116a,122a:Filter

110a,120a: Supply port

110b,120b: outgoing port

120: Second filter system

130: Storage slot

140: Packaging station

160f,160h: Recirculation catheter

Claims (33)

A method for purifying an organic solvent comprises: allowing the organic solvent to pass through a first filter unit and a second filter unit downstream of the first filter unit, and a fourth filter unit downstream of the second filter unit to obtain a purified organic solvent; wherein the first filter unit comprises a first housing and at least one first filter in the first housing, and the first filter comprises a filter medium having a first average pore size; wherein the second filter unit comprises a second housing and at least two second filters in the second housing, the at least two second filters are arranged in parallel in the second housing, and each second filter independently comprises a filter medium having a second average pore size. pore size; wherein the fourth filter unit comprises a fourth housing and at least two fourth filters in the fourth housing, the at least two fourth filters are arranged in parallel in the fourth housing, and each of the fourth filters independently comprises a filter medium having a fourth average pore size; and wherein the number of first filters in the first filter unit is less than the number of second filters in the second filter unit, and the first average pore size is larger than the second average pore size, the number of second filters in the second filter unit is less than the number of fourth filters in the fourth filter unit, and the fourth average pore size is smaller than the second average pore size. A method as claimed in claim 1, wherein the first filter unit comprises a first filter. The method of claim 1, wherein the filter medium in the first filter comprises polypropylene, high-density polyethylene, ultra-high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The method of claim 1, wherein the first average pore size is about 50 nanometers to about 200 nanometers. A method as claimed in claim 1, wherein the second filter unit comprises two or three second filters. The method of claim 1, wherein the filter medium in the second filter comprises polypropylene, high-density polyethylene, ultra-high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The method of claim 1, wherein the second average pore size is about 10 nanometers to about 50 nanometers. The method of claim 1 further comprises allowing the organic solvent to pass through a third filter unit disposed between the first and second filter units, wherein the third filter unit comprises a third housing and at least one third filter in the third housing, the third filter comprises a filter medium having a third average pore size, and the filter medium in the third filter comprises an ion exchange membrane. As in the method of claim 8, wherein the third filter unit comprises one to three third filters. The method of claim 8, wherein the ion exchange membrane in the third filter comprises polypropylene, high-density polyethylene, ultra-high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The method of claim 1 further includes allowing the organic solvent to pass through and discharge the second filter unit to a storage tank. The method of claim 11 further comprises recirculating the organic solvent by moving the organic solvent from the storage tank to the first filter unit and passing the organic solvent through the first and second filter units. The method of claim 1, wherein the fourth filter unit comprises 4 to 14 fourth filters. The method of claim 1, wherein the fourth average pore size is at most about 10 nanometers. The method of claim 1, wherein the filter medium in the fourth filter comprises polypropylene, high-density polyethylene, ultra-high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The method of claim 1 further comprises recirculating the organic solvent by moving the organic solvent discharged from the fourth filter unit to the storage tank and then passing the organic solvent through the fourth filter unit. The method of claim 1 further comprises moving the purified solvent to a packaging station disposed downstream of the fourth filter unit. The method of claim 1, wherein the organic solvent comprises cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 4-methyl-2-pentanol or propylene carbonate. The method of claim 1, wherein the passing of an organic solvent is performed at a flow rate of about 25 to about 170 L/min. A system comprising: a first filter unit, wherein the first filter unit comprises a first housing and at least one first filter in the first housing, and the first filter comprises a filter medium having a first average pore size; a second filter unit, which is downstream of the first filter unit and in fluid communication with the first filter unit, wherein the second filter unit comprises a second housing and at least two second filters in the second housing, the at least two second filters are arranged in parallel in the second housing, and each of the second filters independently comprises a filter medium having a second average pore size; and a fourth filter unit, which is located in the second filter unit. downstream of the element, wherein the fourth filter unit comprises a fourth housing and at least two fourth filters in the fourth housing, the at least two fourth filters are arranged in parallel in the fourth housing, and each of the fourth filters independently comprises a filter medium having a fourth average pore size; wherein the number of first filters in the first filter unit is less than the number of second filters in the second filter unit, the first average pore size is larger than the second average pore size, the number of second filters in the second filter unit is less than the number of fourth filters in the fourth filter unit, and the fourth average pore size is smaller than the second average pore size. A system as claimed in claim 20, wherein the first filter unit comprises a first filter. A system as claimed in claim 20, wherein the filter medium in the first filter comprises polypropylene, high density polyethylene, ultra high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The system of claim 20, wherein the first average pore size is about 50 nanometers to about 200 nanometers. A system as claimed in claim 20, wherein the second filter unit comprises two or three second filters. A system as claimed in claim 20, wherein the filter medium in the second filter comprises polypropylene, high density polyethylene, ultra high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The system of claim 20, wherein the second average pore size is about 10 nanometers to about 50 nanometers. The system of claim 20 further comprises a third filter unit disposed between the first and second filter units, wherein the third filter unit comprises a third housing and at least one third filter in the third housing, the third filter comprises a filter medium having a third average pore size, and the filter medium in the third filter comprises an ion exchange membrane. A system as claimed in claim 27, wherein the third filter unit comprises one to three third filters. A system as claimed in claim 27, wherein the ion exchange membrane in the third filter comprises polypropylene, high density polyethylene, ultra high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer. The system of claim 20 further comprises a storage tank between the second filter unit and the fourth filter unit. A system as claimed in claim 20, wherein the fourth filter unit comprises 4 to 14 fourth filters. The system of claim 20, wherein the fourth average pore size is at most about 10 nanometers. A system as claimed in claim 20, wherein the filter medium in the fourth filter comprises polypropylene, high density polyethylene, ultra high molecular weight polyethylene, nylon, polytetrafluoroethylene or perfluoroalkoxy alkane polymer.